The following references are hereby incorporated by reference herein in their entirety:    1. A. A. Guenkel, “Nitrobenzene and Nitrotoluene”, in J. J. McKetta and W. A. Cunningham (Ed.), “Encyclopedia of Chemical Processing and Design”, Marcel Dekker Inc., New York, (1990) 165-88.    2. M. Dugal, “Nitrobenzene and Nitrotoluenes”, in “Kirk-Othmer Encyclopedia of Chemical Technology, 5th Ed., Vol. 17”, John Wiley & Sons, Inc., (Oct. 14 2005).    3. W. Larbig, “Process for working up effluents containing nitro-hydroxy-aromatic compounds”, U.S. Pat. No. 4,230,567 (1980).    4. J. B. Joshi et al, “Wet Air Oxidation”, Ind. Eng. Chem. Res., 34 (1995) 2-48.    5. S. T. Kolaczkowskia, P. Plucinskia, F. J. Beltranb, F. J. Rivasa, D. B. McLurgh, “Wet air oxidation: a review of process technologies and aspects in reactor design”, Chemical Engineering Journal 73 (1999) 143-160.    6. F. J. Zimmermann, “Waste Disposal”, U.S. Pat. No. 2,665,249, (1950).    7. G. Santarini and J. Y. Boos, “Corrosion of Austenitic Stainless Steels in hot concentrated aqueous NaOH solutions”, Corrosion Science, 19 (1979) 261-81.    8. H. A. Pray, C. E. Schweickert and B. H. Minnich, “Solubility of Hydrogen, Oxygen, Nitrogen, and Helium in Water at Elevated Temperatures”, Ind. Eng. Chem., 44(5) (1952) 1146-51.These references are pertinent to the general state of the art.
During the production of nitrobenzenes and nitrotoluenes small amounts of nitrated partially oxidized by-products are formed (1,2). For production of nitro-benzenes, these nitrated partially oxidized by-products can include compounds such as: mono-nitrophenol, di-nitrophenol, tri-nitrophenol (picric acid), as well as small amounts of nitro-organic acids and poly-nitro-phenols. For production of nitro-toluenes, similar cresol (methyl-phenol) compounds are produced. Because of their partial oxidation, these compounds are more water soluble than the desired nitrated benzene or toluene products, especially when in their salt form. These compounds can therefore be removed from the desired products by washing with alkaline water. While such washing procedures are very effective at providing a clean product chemical, they also generate a wastewater stream contaminated with the partially oxidized nitrated by-products (sometimes referred to as “red water” in the industry due to its pronounced color).
While many wastewater treatment methods are available, biological treatment typically offers considerable cost advantages over other methods. Unfortunately, red water type wastewater is toxic to typical biotreatment systems due to the presence of high concentrations of nitro-hydroxy-aromatic compounds. As used herein, “nitro-hydroxy-aromatic compound” means aromatic compounds having both hydroxyl- and nitro-functional groups, where other groups such as alkyl-groups may or may not also be present. One approach that has been widely adopted within the industry is an anoxic thermal treatment as described in U.S. Pat. No. 4,230,567 (2,3). This approach involves heating the nitro-hydroxy-aromatic compounds in their salt form to 150-500° C. with exclusion of air/oxygen at a pressure of 50-150 bars with a hold time of 5-120 minutes. This anoxic treatment can result in a thermal decomposition of the nitro-hydroxy-aromatic compounds, reducing their concentration to below 20 ppm and thus producing a wastewater that is amenable to biotreatment. The subsequent biotreatment must then remove a significant level of organic carbon (as measured by chemical oxygen demand “COD” or biological oxygen demand “BOD”) and dissolved nitrogen compounds. The suitability of wastewater for subsequent biotreatment can be assessed by examining the BOD/COD ratio.
However, while the nitro-hydroxy-aromatic compounds can be reduced to below 20 ppm, many other organic compounds remain. While these other compounds are much less toxic than nitro-hydroxy-aromatic compounds, some care must be taken in their biotreatment to allow the bacterial population to adapt to the particular mix of compounds and to ensure that the concentrations to which the bacteria are exposed are within their tolerance levels. Normally, at a large chemical facility this is easily handled by blending with other, more easily bio-treated waste streams at a central biotreatment facility, which produces a more benign wastewater and helps to average out variations. However, for a stand alone plant with the output of a treatment system directly coupled to a dedicated biotreatment facility the mix of chemicals in the wastewater and the resulting bio-treatability becomes very important. In such a case, the biotreatment facility must be oversized and carefully designed to allow for upstream process upsets that could lead to higher concentrations of less bio-treatable compounds and even then care must be taken in the operation of the combined system. Thus, a method to more fully treat the wastewater to improve its bio-treatability would be desirable.
An alternative method that could more completely treat the waste solutions is the use of wet-ox (4,5,6). Wet-ox is an air or oxygen fed subcritical oxidation technology for treatment of industrial waste waters containing high concentrations of organic carbon. As a subcritical technology, it operates somewhat below the critical point of water (374° C. and 221 bar) with typical conditions of 125-320° C. and 50-200 bar (4). In theory, through such a high temperature oxidative approach, the level of organic carbon in the wastewater could be decreased by oxidizing it to carbon dioxide. However, as disclosed in U.S. Pat. No. 4,230,567, the additional air or oxygen tends to interfere with the degradation reactions of the nitro-hydroxy-aromatic compounds. This has been reported to result in a treated solution retaining much more than 20 ppm of remaining nitro-hydroxy-aromatic compounds, rendering it non-bio-treatable.
There is a need for practical and cost-effective processes and apparatus for treating water containing organic materials. There are particular needs for such processes that treat waste water containing nitrogen-containing organic compounds such as nitro-hydroxy-aromatic compounds.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.